The use of integrated circuit chips has increased dramatically over the years. Although chip size has decreased and power usage is more efficient than in the past, the practice of mounting multiple, closely spaced chips in modules has required that more emphasis be placed on cooling systems to remove the relatively high density power dissipated by the chips. Liquid coolants are commonly employed in high density applications for cooling the chips.
One problem associated with cooling integrated circuit chips mounted on a substrate is that some of the chips may be tilted or bent and otherwise may have height variations between chips. It is desirable that any cooling system accommodate slightly different chip orientations while providing approximately equal cooling to each chip site.
The prior art has suggested various systems for cooling high powered integrated circuit chips, including those in which multiple chips are arrayed in modules. Previous thermal conductive modules (TCMs) have utilized pistons contained in water cooled housings which contact the chip. Some systems have incorporated water cooled bellows to cool the chip. Such systems are exemplified by IBM Technical Disclosure Bulletin, Vol. 28, No. 11, pp. 4759-4761 (April 1986). Another chip cooling arrangement is suggested in IBM Technical Disclosure Bulletin, Vol. 27, No. 1B, pp. 494-495 (June 1984) in which a copper structure having an internal radial water cooling pattern is conformally interfaced using a layer of a metal alloy with a single semi-conductor chip.
Other systems for cooling high powered chips utilize a cooled foil to cover a plurality of chips. One of such systems, disclosed in U.S. Pat. No. 4,381,032, uses a piston to hold the foil against each chip and a liquid coolant which flows around the piston to remove heat conducted through the foil. Another system which utilizes a heat conductive foil over the integrated circuit chips is disclosed in U.S. Pat. No. 4,531,146. IBM Technical Disclosure Bulletin, Vol. 29, No. 7, p. 2887 (December 1986) discloses yet another system which utilizes a metal heat sink carried on a flexible seal for each chip which is spring loaded downwardly against the chip. The upper surface of the heat sink carries fins and is cooled by a jet of coolant.
In a system disclosed in a recent patent issued to the assignee of this application, Chrysler et al. U.S. Pat. No. 4,928,207, the coolant is carried to each chip through the central bore of a piston which is spaced away from the chip by a spacer having radial vanes. However, this system uses a dielectric coolant which contacts the chips directly and does not create the problems of erosion/corrosion.
Acocella, J. et al. "Copper Device and Use Thereof With Semiconductor Devices" U.S. Pat. No. 5,031,029, the disclosure of which is incorporated herein by reference, discloses a device that contains a copper substrate; a rigidizing layer and/or a metal layer, and a non-graphitic hard carbon layer deposited on the rigidizing layer; and use as a heat sink or piston for electronic components.
Although these systems are suitable in many ways, many require their components to be made to high mechanical tolerances and, consequently, are relatively expensive. This is especially true of those systems employing pistons in thermal conduction modules which form part of the path for heat transfer. Furthermore, the power density of multiple chip modules is expected to increase dramatically, particularly as systems approach very large scale integration (VLSI) densities in bipolar technology. This will require even higher thermal conductance between the chip and the coolant, which the present systems may not be able to accommodate. The use of water based coolants is desirable in this regard. Furthermore, it is necessary that the cooling system be reliable, relatively low in cost to manufacture, and easily replaceable in the field.
The ever increasing performance of the computer chips is associated with increasing chip power and the requirement for higher heat removal rates. The need for an extendable, low cost and high performance cooling system for the multi-chip module has lead to the design of cooling systems, such as, the "Indirect Impingement Cooling" as disclosed in U.S. patent application Ser. No. 07/748,004, filed on Aug. 21, 1991, the disclosure of which is incorporated herein by reference. The cooling system of U.S. patent application Ser. No. 07/748,004, utilizes a fluid, such as water, which is forced to impinge on a thin metal diaphragm, such as a copper foil, which is in direct contact with the chips. The continuous impingement of the forced flow can cause erosion of the foil in the flow path, especially at the stagnation point of the flow opposite each chip. In addition, in spite of the use of deionized water, corrosion of the unprotected thin metal diaphragm and fouling can also occur.
Similarly, on the chip side of the thin metal foil of U.S. patent application Ser. No. 07/748,004, the relative movement of the unprotected thin metal diaphragm and chip due to thermal cycling can cause abrasion of the soft thin metal foil resulting in seizures of the chip corners into the foil. This can impose high stresses on the other components of the chip, such as C4s, lead joints, etc.
This invention overcomes those erosion and/or corrosion problems of an unprotected metallic foil by providing an erosion/corrosion resistant coating on one side of the metallic foil that will be exposed to the fluid impingement. And a similar erosion/corrosion resistant coating is provided on the opposite side of the metallic foil where the normal thermal cycling of the chip might damage the unprotected metallic foil.